1. Field of the Invention
The present invention relates to RFID (radio frequency identification) tagging systems and more particularly, to a auxiliary antenna array for increasing the range of a RFID system for detecting foreign objects in a surgical patient wherein the auxiliary antenna array consists of pairs of antennae and associated electronics placed in a mattress situated on top of an operating table.
2. Description of Prior Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The problem of leaving foreign objects, such as surgical instruments and sponges, in patients after surgery has been of great concern ever since modern surgery began. A foreign object present in a patient after surgery can lead to illness or death. Further, it also raises serious medical malpractice issues.
Accordingly, various systems have been tried to prevent foreign objects from being left off in patents after surgery. Such systems include manually or automatically counting the surgical instruments and sponges used in a surgical procedure before and after surgery and comparing the counts to insure that all instruments and sponges used in the procedure are accounted for. However, such systems do not produce completely satisfactory results as they are dependant upon human beings for accuracy and human beings are prone to make errors, especially when functioning under pressure or adverse conditions.
Metal objects, such as surgical instruments, can be detected by X-ray or other scanning techniques. However, such detection systems require costly and expensive equipment, pose a danger to unprotected personnel, and subject patients to potentially harmful radiation. Further, some systems, such as x-ray scanners, are unable to detect non-metallic objects.
RFID tagging has also been suggested for use in tracking and counting surgical instrument and sponges. Radio frequency identification (RFID) tags emit a radio frequency signal when excited by electromagnetic energy from a transmitting antenna. The emitted signal can include a coded identification number that represents a particular object, such as a surgical instrument or sponge. The emitted signal is received by a receiving antenna and processed by a computer to decode the identification number. The identification number is unique to a particular object and there permits automated tracking of all objects utilized during surgery with great accuracy once the RF signal from the excited tag is received.
One of the benefits of such a system is that it is non-evasive. The body of the patient can be quickly and easily scanned at the end of the surgical procedure to ensure all tagged instruments and sponges have been removed form the patient. The scanning can be performed by a conventional hand-held device or wand that contains a transmitting antenna, a receiving antenna, signal processing circuitry and a display or other audible or visual indicating device.
However, conventional systems of this type are not entirely reliable because they do not always receive the RF signal from the tag. They therefore require repeated scanning of the body at close range and in different orientations to provide reliable results. Properties of RFID tags that effect instrument scanning are: (a) the maximum distance between antenna and RFID tag is a function of the frequency of the signal; (b) signal attenuation due to water and soft tissue in the body is inversely dependant upon the frequency of the signal; (c) the received signal is strongest when the tag is perpendicular to the movement of the receiving antenna; (d) the metal of surgical instruments tends to block radio frequency waves; and (e) the size of the RFID tag is a function of the frequency of the emitted signal.
Those properties necessitate the use of small, low frequency RFID tags for detecting objects such as surgical instruments or sponges in the body. However, even when those types of RFID tags are utilized, successful scanning of the tag is limited by patient size and instrument orientation. Finding a retained instrument or sponge in the body requires scanning the patient multiple times and changing the antenna orientation for each scan. Accordingly, conventional equipment utilizing RFID tags for detecting the presence of foreign objects in a patient after surgery have not proved to be totally satisfactory.
The present invention greatly improves the success rate for detecting a retained instrument or sponge, utilizing small, low frequency RFID tags, by utilizing auxiliary receiving antennae to increase the ability of the system to receive the signal transmitted from the RFID tag. The antennae are situated in an array that is preferably mounted within a standard size mattress pad adapted to be situated beneath the patient on the operating table. The pad may be a single unit or consist of one or more removable sections to facilitate patient placement for various surgical procedures. The pad contains multiple receiving antennae arranged in pairs and associated electronics.
The mattress pad with the auxiliary antenna array replaces the pad normally used on an operating table. Before the surgical procedure begins, each of the instruments and sponges in the room is provided with an encoded RFID tag. The patient lies on top of the pad as in any surgical procedure. At the end of the procedure, before the incision is closed, the patient is scanned with a hand-held transducer containing both a transmitting antenna and receiving antenna, along with processing circuitry.
The transmitting antenna in the transducer generates a signal that excites any RFID tag in the body, which then emits a radio frequency signal. The signal generated by the RFID tag is received by the receiving antenna in the transducer and/or by one or more of the receiving antennae of the auxiliary antenna array within the pad below the patient. The auxiliary antenna array greatly increases the ability of the system to receive the RFID signal from the tagged object, regardless of the orientation of the surgical instrument or sponge within the body, or patient size, without the necessity for multiple scans.
It is, therefore, a prime object of the present invention to provide an improved system for detecting foreign objects in a patient after surgery.
It is another object of the present invention to provide an RFID tagging system for detecting foreign objects in a patient utilizing an auxiliary antenna array to increase the ability of the system to receive a signal from the RFID tagged object.
It is another object of the present invention to provide a system for detecting foreign objects in a patient on an operating table that utilizes small, low frequency RFID tags.
It is another object of the present invention to provide a system for detecting foreign objects in a patient on an operating table that reduces the necessity for scanning the patient multiple times using different antenna orientations.
It is another object of the present invention to provide a system for detecting foreign objects in a patient on an operating table that utilizes an auxiliary antenna array situated in a mattress pad of the type normally used on an operating table.